Is it possible for the plugin to recognize the quit command in console? I don't always use the restart command, if no one is connected. If it's not possible I guess I could always restart for 1 second.

The quit command would be handled via the plugin already with OnServerShutdown.

Thanks Wulf, good to know this can be done. I retested it, and nothing was sent to discord. So I believe it's not working. Can anyone else confirm?

How are you shutting down the server? OnServerShutdown is only triggered if the server shuts down gracefully, not via a forced restart via a control panel or process kill.

I'm running the quit command from console. 

That would trigger the OnServerShutdown process, but may not have enough time to complete the webrequest to Discord.